The invention relates to a spring device for balancing the vertical movements of amount structure of a multi-joint robot, and more particularly relates to a spring device including one or a plurality of tension coil springs for balancing the vertical movements of amount structure of a multi-joint robot, the mount structure having a predetermined weight and having a plurality of jointed operating parts mounted thereon. A conventional industrial multi-joint robot is disclosed in the same applicant's Japanese Utility Registration Application, laid open No. 6-74237 under the title "A Feed Mechanism of Robot", wherein tension coil springs are used to balance the vertical up and down movements of a mount structure of the multi-joint robot having a predetermined weight, so that the mount structure may be driven with a little output. Otherwise, it is generally known to utilize a weight for balancing the weight of the mount structure of the multi-joint robot. In this case, however, the inertia is an undesirable element, and further the device becomes bulky.
In order to effectively balance the up and down movements of the mount structure of the multi-joint robot, it is required to effectively utilize the tension coil springs having the specified properties. Namely the tensile load of the tension coil springs is approximately equivalent to the weight of the mount structure and further the tensile load is constant in the entire region where the mount structure is moved up and down. In order to satisfy such requirement, the tension coil springs are often lengthened even though the springs are bent at the intermediate part or parts thereof, and as the result, the device becomes bulky accordingly. It has been desired to make the robot mechanically compact and smaller while the mentioned requirement is satisfied.